The goal of this proposal is to characterize the transcriptional regulatory circuits and control the development and maintenance of the vertebrate skeletal muscle phenotype. Characterization of the novel bHLG factor (Mist1) and the muscle-specific LIM protein (MLP) as well as identifying the target genes of the MRFs during the establishment of the myogenic lineage is critical to dissecting the regulatory networks that control skeletal myogenesis. The PI proposes to: 1) examine how Mist1 inhibits MRF activity; 2) establish the mechanism(s) by which the muscle LIM protein, MSP, enhances MRF activity and 3) identify true myoblast-specific genes that are regulated by the MRFs.